1. Field of the Invention
The present invention relates generally to an apparatus which provides a seal between two surfaces, and specifically to an apparatus which seals the ends of two optical fiber cables inside a casing to prevent damage to optical fibers and optical attenuation when the casing is submerged in water and exposed to hydrogen. The present invention is directed at providing a seal at an end of the casing.
2. Description of the Prior Art
In the prior art, submarine optical cable junctions are known for connecting two cables underwater. In such a submarine optical cable junction, optical fibers from one cable are physically connected to optical fibers of another cable, disposed underwater, and subjected to water pressure in excess of 10,150 pounds per square inch.
In view of this, the submarine optical cable junction typically suffers from problems caused by hydrogen entering into the cable junction that adversely affects the optical fibers in the two cables that are exposed in the cable junction. The hydrogen is generated near the cable junction from galvanic corrosion of metal parts, magnetohydrodynamic effects, and microbial activity near the cable junction. The hydrogen causes optical loss in the optical fiber, which is known in the art as hydrogen induced attenuation. If hydrogen penetrates a significant distance along the optical fibers, then the hydrogen causes a significant amount of hydrogen induced attenuation in the optical fiber.
FIG. 1 shows one end of a prior art cable junction generally indicated as 8 having a cable 10 sealed inside a tubular stainless steel casing 12. The cable 10 is connected to another cable similarly sealed inside the casing 12 but not shown in FIG. 1. The cable junction 8 is substantially symmetrical, and for the purpose of this discussion only one end is shown and described herein. The cable 10 typically has a capillary tube 16 which contains a water-blocking compound therein. The water-blocking compound may contain a hydrogen-absorbing compound, which may delay the onset of hydrogen induced attenuation depending upon the absorption capacity of the compound, the degree to which the compound fills the capillary tube 16, and the applied hydrogen pressure. However, hydrogen inevitably enters the capillary tube 16.
The cable 10 comprises a protective sheath 14, a power conductor 15, a capillary tube 16, within which are housed the optical fibers (not shown), and strength members 17. The cable 10 is secured to the anchorage 20 by clamping the strength members 17 to the anchorage 20 via a ferrule 22, a retaining washer 23, and a retaining nut 24. The mounting block 21 provides support for the capillary tube 16. The mounting block 21 is held against the anchorage 20 by stopper screws 31. The anchorage 20 is in turn fixed relative to the casing 12 via the anchorage/casing threaded joint 33 and the loading ring 38. The loading ring 38 is threaded on the anchorage 20 by engaging a torque wrench (not shown) in blind holes 38a, for turning the loading ring 38 on the threads 85.
To secure the cable 10 to the anchorage 20, the protective sheath 14 is removed from the cable 10 to expose the power conductor 15. A compression body 26 and a sleeve portion 27 are compressed against the power conductor 15 and the anchorage 20 by threaded cap nut 28 to secure cable 10 to anchorage 20.
The prior art suffers from problems related to hydrogen entering into the cable junction 8. One such problem is that the anchorage/casing threaded joint 33 does not provide an effective seal with regard to hydrogen. Therefore, hydrogen can leak into the casing 12 between the casing 12 and the loading ring 38 at a junction generally indicated as "A" in FIG. 1. In addition, hydrogen can leak into the casing 12 between the anchorage 20 and the loading ring 38 at a junction generally indicated as "B" in FIG. 1. Furthermore, there is no sealing member between the tubular stainless steel casing 12 and the loading ring 38 at the junction A.